Biomass has been a primary source of energy over much of human history. During the late 1800's and 1900's the proportion of the world's energy sourced from biomass dropped, as the commercial development and utilization of fossil fuels occurred, and markets for coal and petroleum products dominated. Nevertheless, some 15% of the world's energy continues to be sourced from biomass, and in developing countries the contribution of biomass is much higher at 38%. In addition, there has been a new awareness of the impact of the utilization of fossil fuels on the environment. In particular, the contribution of greenhouse gases, as a result of consuming fossil fuels.
Biomass, such as wood, wood residues, and agricultural residues, can be converted to useful products, e.g., fuels or chemicals, by thermal or catalytic conversion. An example of thermal conversion is pyrolysis where the biomass is converted to a liquid and char, along with a gaseous co-product by the action of heat in essentially the absence of oxygen.
In a generic sense, pyrolysis is the conversion of biomass to a liquid and/or char by the action of heat, typically without involving any significant level of direct combustion of the biomass feedstock in the primary conversion unit.
Historically, pyrolysis was a relatively slow process where the resulting liquid product was a viscous tar and “pyroligneous” liquor. Conventional slow pyrolysis has typically taken place at temperatures below 400° C., and over long processing times ranging from several seconds to minutes or even hours with the primary intent to produce mainly charcoal and producing liquids and gases as by-products.
A more modern form of pyrolysis, or rapid thermal conversion, was discovered in the late 1970's when researchers noted that an extremely high yield of a light, pourable liquid was possible from biomass. In fact, liquid yields approaching 80% of the weight of the input of a woody biomass material were possible if conversion was allowed to take place over a very short time period, typically less than 5 seconds.
The homogeneous liquid product from this rapid pyrolysis, which has the appearance of a light to medium petroleum fuel oil, can be considered renewable oil. Renewable oil is suitable as a fuel for clean, controlled combustion in boilers, and for use in diesel and stationary turbines. This is in stark contrast to slow pyrolysis, which produces a thick, low quality, two-phase tar-aqueous mixture in very low yields.
In practice, the short residence time pyrolysis of biomass causes the major part of its organic material to be instantaneously transformed into a vapor phase. This vapor phase contains both non-condensable gases (including methane, hydrogen, carbon monoxide, carbon dioxide and olefins) and condensable vapors. It is the condensable vapors that constitute the final liquid product, when condensed and recovered, and the yield and value of this liquid is a strong function of the method and efficiency of the downstream capture and recovery system.
Given the fact that there is a limited availability of hydrocarbon crude and an ever increasing demand for energy, particularly liquid transportation fuels, alternative sources are therefore required. The abundance and sustainability of biomass makes this renewable feedstock an attractive option to supplement the future demand for petroleum. The difficulty with biomass is the fact that it contains oxygen, unlike conventional hydrocarbon fuels, and historically has not been readily convertible into a form that can be easily integrated into existing hydrocarbon based infrastructure.
A significant amount of work has been done to investigate the production of liquid hydrocarbon fuels from biomass by various thermal and thermocatalytic schemes. U.S. Pat. Nos. 5,792,340; 5,961,786; Lappas et al., Biomass Pyrolysis in a Circulating Fluid Bed Reactor for the Production of Fuels and Chemicals, Fuel 81 (2002), 2087-2095); and Samolada et al., Catalyst Evaluation for Catalytic Biomass Pyroloysis, Fuel & Energy 2000, 14, 1161-1167, describe the direct processing of biomass or other oxygenated carbonaceous feedstocks in a circulating fluid bed reactor using a catalyst (zeolite FCC catalyst) as the solid circulating media in an effort to directly deoxygenate the biomass and produce transportation fuels or fuel blends, as well as other hydrocarbons. Although some hydrocarbon products were produced, the yields were unacceptably low, and there was a high yield of char or coke and by-product gas produced. In addition, there were frequent issues with reactor fouling and plugging, and other serious technical difficulties associated with catalyst performance. Not only were the liquid yields lower, much of liquid product produced would require further upgrading and treatment to enable any direct immediate use in place of fossil fuel-based hydrocarbons.
Given the above limitations, another alternative for hydrocarbon production from biomass is to convert solid biomass first into a thermally-produced or thermocatalytically-produced liquid, and then feed this neat liquid (i.e. 100% liquid biomass product) into a circulating fluid bed reactor using a FCC catalyst or other appropriate catalyst as the solid circulating media (Adjaye et al., Production of Hydrocarbons by Catalytic Upgrading of a Fast Pyrolysis Bio-oil, Fuel Processing Technology 45 (1995), 185-192). Again, in this case, unacceptable hydrocarbon yields were achieved, reactor plugging and fouling was often evident, and much of the feedstock was converted to char/coke, gas and an oxygen-rich liquid that tended to separate into different liquid phases.
The use of catalytic cracking of a solid or liquid biomass, a biomass-derived vapor, or a thermally-produced liquid as a means to produce hydrocarbons from oxygenated biomass is technically complex, relatively inefficient, and produces significant amounts of low value byproducts. To solve the catalyst and yield issues, researchers looked at stand-alone upgrading pathways where biomass-derived liquids could be converted to liquid hydrocarbons using hydrogen addition and catalyst systems in conversion systems that were tailored specifically for the processing of oxygenated materials (Elliott, Historical Developments in Hydroprocessing Bio-oils, Energy & Fuels 2007, 21, 1792-1815). Although technically feasible, the large economies-of-scale and the technical complexities and costs associated with high-pressure multi-stage hydrogen addition (required for complete conversion to liquid hydrocarbon fuels) are severely limiting and generally viewed as unacceptable.
As a means to overcome the technical and economic limitations associated with full stand-alone biomass upgrading to transportation fuels, researchers (de Miguel Mercader, Pyrolysis Oil Upgrading for Co-Processing in Standard Refinery Units, Ph.D Thesis, University of Twente, 2010 (“Mercader”); Fogassy et al., Biomass Derived Feedstock Co-Processing with VGO for Hybrid Fule Production in FCC Units, Institut de Recherches sur la Catalyse et l'Environnement de Lyon, UMR5236 CNRS-UCBL (“Fogassy”); Gutierrez et al., Co-Processing of Upgraded Bio-Liquids in Standard Refinery Units—Fundamentals, 15th European Biomass Conference & Exhibition, Berlin May 7-11, 2007) are looking at various schemes for partial upgrading of the oxygenated biomass to reduce oxygen, followed by the co-processing of this intermediate biomass product with petroleum feedstocks in existing petroleum refinery operations. These initiatives are all focused on hydrodeoxygenation of the biomass-derived liquid prior to co-processing with petroleum, and are predicated on the consideration that hydrotreatment of the thermally produced liquid is necessary prior to petroleum co-processing in order to avoid rapid FCC catalyst deactivation and reactor fouling, and to preclude excessive coke and gas production. Hence, the published studies and prior art include the co-processing of petroleum in fluid catalytic cracking (FCC) refinery units with upgraded liquids that have been hydrotreated after their initial thermal production from biomass.
The early FCC units traditionally used dense phase bed reactor systems to enable good contact between the catalyst and the hydrocarbon feedstock. Long residence times were required to ensure sufficient conversion of the feedstock to the desired product. As catalyst systems improved and the catalyst became more active, the FCC was redesigned to incorporate a riser configuration. The riser configuration enabled contact times between the catalyst and hydrocarbon feedstock to be reduced to somewhere around 2 to 3 seconds (does not include any residence time in the reactor vessel or termination section).
One drawback of many, if not most of the early FCC designs was the riser termination systems that essentially linked the riser to an open reactor vessel that housed the solids separation devices. It had been recognized for several years that significant post riser thermal cracking occurs in commercial FCC units resulting in the substantial production of dry gas and other lower value products. The two mechanisms by which this occurs are through thermal and dilute catalytic cracking. Thermal cracking results from extended residence times of hydrocarbon vapors in the reactor disengaging area, and leads to high dry gas yields via non-selective free radical cracking mechanisms. Dilute phase catalytic cracking results from extended contact between catalyst and hydrocarbon vapors downstream of the riser. While much of this was eliminated in the transition from bed to riser cracking, there is still a substantial amount that can occur in the dilute phase due to significant catalyst holdup which occurs without an advanced termination system design.
Many FCC vendors and licensors offer advanced riser termination systems to minimize post-riser cracking, and many if not most units have implemented these in both new unit and revamp applications. In addition, some refiners have implemented their own “in-house” designs for the same purpose. Given the complexity and diversity of FCC units as well as new unit design differences, there are many variations of these advanced termination systems such as “closed” cyclones, “close-coupled” cyclones, “direct coupled” cyclones, “high containment systems”, “vortex separation system”, etc. There are differences in the specific designs, and some may be more appropriate for specific unit configurations than others, but all serve the same fundamental purpose of reducing the undesirable post-riser reactions.
Contact time of the catalyst with the feedstock is comprised of the residence time in the riser and often includes the residence time in the advanced riser termination system as described above. Typical riser residence times are about 2 to 3 seconds and the additional termination system residence time may be about 1 to 2 seconds. This leads to an overall catalyst contact time of about 3 to 5 seconds.
One innovative embodiment that forms part of the present application may be to processes employing thermally-produced liquids in conjunction with petroleum based materials in FCCs or field upgrader operations. For example, a method that includes the co-processing of an non-hydrotreated biomass derived liquid in small amounts with VGO or other crude oil based liquids in the FCC or field upgrader operations.
Another innovative embodiment that forms part of the present application may be for biomass conversion that the prior art has overlooked and intentionally avoided: the co-processing of non-upgraded, thermally-produced liquid with hydrocarbons in a manner which removes the complexity of intermediate upgrading steps and yet may be still compatible with crude oil feedstock processing. As already indicated, the prior art has clearly shown that non-treated, thermally-produced biomass liquids are not suitable for conversion to liquid hydrocarbons directly in FCC and other catalytic conversion systems. Therefore when various schemes of co-processing with petroleum in existing refinery operations are considered in the prior art, including FCC co-processing, the co-processing of non-upgraded, non-treated thermal biomass liquids may be excluded from these co-processing options (Mercader; Fogassy). However, as set forth in the present disclosure, unexpected technical and economic benefits are in fact evident in the co-processing of thermally-derived biomass products with petroleum feedstocks in various refinery operations.